Optical connector, a communication system and a method of connecting a user circuit to an optical transceiver

ABSTRACT

The invention provides an optical connector for connecting a user circuit to an optical backplane, in use the connector being adapted for mounting on a user circuit. The connector comprises an active or passive photonic interface through which optical signals may be transmitted and received between a user circuit and a said optical backplane. The connector further is comprised of a primary aligner for engagement with a corresponding aligner on a backplane to ensure alignment of the optical interface with the backplane, and a support for supporting the aligner and/or the optical interface on the connector. The support is selected to enable relative movement between a user circuit to which the connector is connected in use and the aligner and/or the optical interface. The support is preferably a flexible printed circuit board.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase of PCT/GB2006/001941, filed May 30,2006, which in turn claims priority to U.S. provisional application No.60/686,053, filed Jun. 1, 2005, the contents of both of which areincorporated herein in their entirety by reference.

The present invention relates to an optical connector, a communicationsystem and a method of connecting a user circuit to an opticalbackplane.

Optical backplanes are known. An example of such a backplane isdescribed in our co-pending patent application no. U.S. 60/569,626 theentire contents of which are hereby incorporated by reference. Asdisclosed in U.S. Pat. No. 6,569,626, in use, a number of user circuitsare connected to an optical backplane. Communication between the usercircuits is achieved by the transmission of optical signals from onecircuit to the backplane and then along the backplane and to its desireddestination, i.e. one of the other user circuits. It is important thatthe connection between each of the user circuits and the opticalbackplane is such that as much as possible of the desired light forminga signal from one of the user circuits is coupled into the opticalbackplane.

To achieve accurate alignment of the optical transceivers and thebackplane to which they are connected, complex adjustment processes arerequired. Typically a trial and error procedure is used whereby a usercircuit is connected to the backplane and the user circuit is thenmanipulated until a satisfactory quality of signal transmission alongthe backplane is achieved. This is time consuming and thereforeexpensive.

There is a need for an optical connector suitable for connecting a usercircuit to an optical backplane, the connector being low cost andsuitable for Very Short Reach (VSR) optical applications.

According to a first aspect of the present invention, there is providedan optical connector for connecting a user circuit to an opticalbackplane, in use the connector being adapted for mounting on a usercircuit or on a backplane, the connector comprising: an opticalinterface through which optical signals may be transmitted and receivedbetween a user circuit and a said optical backplane; a primary alignerfor engagement with a corresponding aligner on a backplane or usercircuit to ensure alignment of the optical interface with the backplaneor user circuit; and a support for supporting the aligner and/or theoptical interface on the connector, the support being selected to enablerelative movement between a user circuit or backplane to which theconnector is connected in use and the primary aligner and/or the opticalinterface.

In an embodiment, the invention provides an optical connection systembased on the use of an optical interface and an aligner that are movablewith respect to the user circuit to which they are connected. In anexample, the optical interface and aligner are assembled on a flexibleprinted circuit board (PCB) material, to allow the active opticalcomponents in the user circuit to be mechanically aligned with anoptical interface in a receptacle optical system such as an opticalbackplane. In embodiments, the invention thus exploits the mechanicalproperties of flexible PCB to accommodate a free-floating active opticalcomponent system within a transceiver connector module, such that themodule remains rigid with respect to the user circuit on which it issupported, whereas the optical interface and aligner can befree-floating and, mechanically translated into and out of engagementwith an interface on the receptacle optical backplane.

Preferably, the connector comprises an optical transceiver on board theconnector.

In a particularly preferred embodiment, a connector is provided thatmakes possible the implementation of optical connection systems betweenelectronic daughter boards and an optical PCB or backplane in a largerack system, without compromising the critical optical alignmentrequirement inherent to the systems. In other words, the connector isprovided such that engagement with a backplane in a way that will ensuregood optical communication may be performed simply and manually by anunskilled user.

According to a second aspect of the present invention, there is provideda method of connecting a user circuit to an optical backplane, themethod comprising: providing a user circuit having a connector arrangedthereon, the connector being a connector according to the first aspectof the present invention; providing an optical backplane having one ormore sockets for receiving a connector; engaging the connector withinthe socket of the backplane.

According to a third aspect of the present invention, there is provideda communication system comprising: an optical backplane for receivingone or more user circuits and enabling optical communicationtherebetween; one or more user circuits for connection to the opticalbackplane; and, a connector for connecting the or each user circuit tothe optical backplane, wherein the connector is an optical connectoraccording to the first aspect of the present invention.

The flexible optical connector could be mounted on the optical backplanefor connection to a user circuit or alternatively mounted on the usercircuit for connection to an optical backplane. In each case thecorresponding arrangement of plug/socket etc may be configuredaccordingly.

According to a fourth aspect of the present invention, there is providedan optical transceiver for transmitting light into or receiving lightfrom an optical backplane, the transceiver comprising a light generatoror a light sensitive receiver and an optical arrangement for imaginglight received from or transmitted to an optical backplane when in use,the optical arrangement comprising a flat lens.

In an embodiment the optical transceiver includes a graded index lens orgraded index lens array. Such an arrangement is flat in that it has aflat outer surface. This enables accurate alignment of the lens againstanother flat surface such as the optical waveguide interface of anoptical backplane.

Examples of the present invention will now be described in detail, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an optical connector and an opticalbackplane for receiving the connector;

FIG. 2 is a schematic representation showing a user circuit and aconnector in engagement with an optical backplane;

FIG. 3 is a section through an optical connector connecting an opticalbackplane and a user circuit in a first mode of operation;

FIG. 4 is a section through the optical connector of FIG. 3 in a secondconfiguration;

FIG. 5 is a schematic representation of an optical backplane with nouser circuits connected to it;

FIG. 6 shows a longitudinal cross-section through an example of aflexible circuit board suitable for use in the connector shown in anddescribed with reference to any of FIGS. 1 to 4; and

FIG. 7 shows a plan view of a schematic representation of a GRIN lensarray arranged on an array holder.

Before describing in detail examples of embodiments of connectorsaccording to one aspect of the present invention it is pointed out thatwhere terms such as “upward”, “downward”, “up”, “down” etc. are usedthese are in reference to the layout of the examples shown in theFigures. They are clearly not limiting and can be interpreted asrelating to relative positions of the components described as shown inthe accompanying Figures.

FIG. 1 shows a perspective view of part of an optical backplane 2 andpart of a user circuit 4 together with a connector 6 coupled to the usercircuit 4. The optical backplane includes one or more optical waveguides8, such as a polymer waveguide, arranged on it. In the example shown,the optical waveguide is within a parallel array of optical waveguides.Other possible waveguide arrangements could be used such asnon-parallel, curved, split, cross-over, or any other optical waveguidepattern which supports optical communication.

A mounting 10 is provided connected to the optical backplane 2. Themounting 10 has an opening 12 for receiving one end of the connector 6.The mounting includes or has a space for a waveguide interface (notshown). As will be explained below, the waveguide interface serves toreceive optical signals from a user circuit and couple them to thewaveguide and vice versa.

The connector 6 will be described in more detail below but generally, itcomprises an optical interface, e.g. a photonic interface 14 that in useis aligned with the waveguide or waveguides 8 of the optical backplane 2to enable optical communication between the photonic interface and theoptical backplane 2. It is important to note that in a multiplewaveguide arrangement, simultaneous alignment of the parallel opticswithin the photonic interface may be desired with all the waveguides.The optical interface may be an active or a passive photonic interfacefor transmitting and receiving light signals.

A housing (not shown) surrounds the components of the connector. Thehousing is preferably a rigid structure that provides physicalprotection to the components of the connector. It will be appreciatedthat the photonic interface 14 is also in communication with a usercircuit 4 so that the connector 6 enables communication between the usercircuit 4 and the optical backplane 2. Thus, the user circuit 4 is ableto communicate with other user circuits that are also connected to theoptical backplane 2 by the transmission and reception of optical signalsalong the waveguide 8.

As will be explained below, the optical interface includes one or morelenses to image or illuminate light passing through it. By providing animaging lens or lenses optical coupling to a small waveguide is improvedas all light is imaged into a small image point.

The opening 12 in the mounting 10 is sized to receive the connector 6and in particular the distal end of the housing of the connector 6. Atthe distal end, a locking plug 28 is provided. It is the locking plug 28that engages with the opening 12 upon connection of a user circuit tothe backplane. In the example shown the connector utilises a cam andspring latch mechanism in combination with a flexible PCB substrate,both to lock the connector in place and to manipulate the position ofthe photonic interface 14. Thus the connector ensures that the photonicinterface 14 is in suitable alignment with the optical backplane 2 andthe waveguide or waveguides 8 thereon. In combination with the geometryof the connector housing, this enables controlled engagement anddisengagement of the photonic interface 14 with the waveguide 8 on theoptical backplane.

In the example shown, the connector 6 has a flexible circuit board 16 onwhich is mounted the photonic interface 14. The housing (not shown)surrounds the components of the connector. The flexible substrate isthus surrounded by the connector housing and is free within limits tomove within the housing. The connector includes an aligner referred toherein after as primary alignment device 18. In the example shown in theFigures, the primary alignment device 18 comprises a pair of pins suchas standard MT pins that are sized to engage with a pin receiver 19. Asshown clearly in FIGS. 3 and 4, the pin receiver has slots 30dimensioned to receive the pins. Other suitable alignment devices may beused. It is preferred that the pins 18 are shaped to make easier theirentry into the slots 30. For example the pins may be chamfered orsmoothly tapered at the top, i.e. first point of pin entry. Of course,the pin/socket relationship may be reversed such that pins are providedon the backplane 2 for engagement within sockets in the connector 6.Indeed, any suitable means of alignment may be utilised.

By virtue of the arrangement of the photonic interface 14 on theflexible circuit board 16, the alignment device 18 and the photonicinterface 14 is movable with respect to the connector and therefore withrespect to the user circuit 4 to which, in use, the connector ismounted. This ensures that the optical connection between the usercircuit 4 and the optical backplane 2 can be precisely aligned so as toensure good communication between the two.

With reference to FIG. 2, the example shown therein will now bedescribed in detail. As with the example shown in FIG. 1, the connector6 includes a flexible circuit board 16. A controller for controllingmovement of the flexible circuit board 16 and the photonic interfacedevice 14 is provided. In the example shown in FIGS. 1 to 4, thecontroller comprises a cam 21 connected both to a cam lever 20 and a camhandle 22. Upon rotation of the cam handle 22 in a counter-clockwisedirection (as shown in FIGS. 1 to 3) the cam lever 20 is urged upwardsthereby forcing the photonic interface 14 upwards too. Thus, theflexibility of the circuit board 16 must be sufficient to enable therelative movement of the photonic interface 14 with respect to theconnector 6 upon activation of the controller (i.e. upon rotation of thecam handle 22).

It will be appreciated that the cam arrangement described above ismerely an example of a suitable controller for controlling movement ofthe flexible circuit board and the photonic interface unit. Any suitablecontroller may be used. For example, an electromagnetic device may beused.

Referring to FIG. 3, a spring system 24 is provided located generallywithin the locking plug 28. The spring system 24 includes one or moresprings 26. The springs 26 accommodate limited movement of the photonicinterface 14 in any direction and over-travel upon mechanical engagementof the photonic interface 14 with the polymer waveguide interface 18 onthe optical backplane 2.

The spring system 24 is arranged in engagement with a locking plug 28shown clearly in FIGS. 3 and 4. In the example shown, the locking plugand all its subsidiary components on the connector are supported by thecam lever 20. As explained above, the cam lever provides the verticaltranslation that is necessary to bring the photonic interface 14 intoregistration with the optical backplane receptacle so that opticalcommunication is enabled between the user circuit 4 and the waveguide 8.The cam lever 20 in turn is controlled by the rotation of theuser-operated cam handle 22 located on the exterior of the connectorhousing (not shown).

In the example shown and described so far, the optical interface is aphotonic interface including an optical transceiver. It will beappreciated that the optical interface need not include a transceiver.Indeed, the connector could have flexible waveguides arranged thereon tocouple light to and from a transceiver arranged elsewhere e.g. on theuser circuit.

Referring now to FIGS. 3 and 4, an engagement/disengagement cycle willnow be described for the connector. Initially, the connector (connectedto a user circuit 4) is brought into engagement with the opening 12 onthe optical backplane 2. In other words, the locking plug 28 is forcedto mate with the opening 12 in the mounting 10. A secondary aligner oralignment means (the MT pins in this example being the primary aligneror alignment means) are provided to ensure that the connector is in ageneral position such that engagement between the pins and the socketsis possible. The secondary alignment means may comprise any suitablearrangement such as guide rails. These could be provided on the opticalbackplane receptacle to enable the correct alignment of the locking plug28 in the opening 12.

Once the locking plug 28 is in place, the cam handle 22 is operated. Inthe example shown this is achieved by anti-clockwise rotation of the camhandle. The cam lever 20 is raised, thus raising the locking plug andforcing upward the distal end of the flexible circuit 16 which supportsthe photonic interface. The locking plug engages further with thelocking receptacle 12 on the optical backplane. Then, the alignmentmeans (pins 18 in this example) are guided into the pin receiving slots30 on the backplane. Thus, the photonic interface is forced intoalignment with the waveguide interface of the optical backplane.

In view of the fact that the engagement is guided by the alignment ofthe pins 18 and the pin receptacles 30, and the locking plug 28 andlocking plug receptacle 12, this is not a skilled process. Accordingly,an unskilled user is able correctly to align the optical interface 14 onthe connector with the waveguide 8 on the optical backplane. FIG. 3shows the user circuit engaged with the optical backplane. The cam lever20 is raised so that the pins 18 are securely located within the pinreceptacles 30 on the optical backplane.

Referring now to FIG. 4, the cam handle 22 is again operated. This timeit is rotated in a clockwise direction. The pins 18 are disengaged fromthe pin receptacles 30 on the optical backplane. The locking plug 28 isdisengaged from the locking receptacle 12. The user circuit 4 and theconnector can now be manually withdrawn from the optical backplane.

The example shown in and described with reference to FIGS. 1 to 4 is onespecific example of a connector suitable for enabling the manualalignment of an optical interface 14 with an optical waveguide 8 on anoptical backplane 2. It will be appreciated that other suitable devicescould be used. It is important that the photonic interface 14 is movablewith respect to the user circuit 4. In the examples shown, this isachieved by the provision of a flexible circuit board 16 on which thephotonic interface is mounted.

FIG. 5 shows a schematic representation of an optical backplane 2 havingtwo optical mounts 10 arranged thereon. One or more optical waveguides 8such as a polymer waveguide is or are provided on the optical backplane.Any suitable type of waveguide may be used. For example, silica, glass,transparent ceramic or an optical fibre waveguide could be used. Theoptical mounts 10 are as described above with reference to FIGS. 1 to 4.It will be appreciated that when a first user circuit is connected toone of the optical mounts 10 shown in FIG. 5 and a second user circuitis connected to the second optical mount 10 in FIG. 5, opticalcommunication between the two user circuits will be possible along theoptical waveguides 8.

FIG. 6 shows a longitudinal cross-section through an example of aflexible circuit board suitable for use in the connector shown in anddescribed with reference to any of FIGS. 1 to 4. The flexible circuitboard 16 has mounted at one end a photonic interface unit 14. Thephotonic interface unit 14 includes drivers 32, a heat sink 24 and an MTpin block 36. As explained above the MT pins enable precise alignment ofthe photonic interface unit 14 with the waveguide or waveguides 8 on theoptical backplane 2.

In the examples shown in FIG. 6, a graded index (GRIN) lens array holder38 is provided. Within the holder 38, a number of GRIN lens are mounted.These are particularly suitable for use in the photonic interface unit.The reason that they are particularly suitable for use is that they havea substantially flat upper surface i.e. the surface opposite the surfacethat engages the flexible circuit board. When the connector is actuallyconnected to an optical backplane and therefore the photonic interfaceunit is engaged with an optical receptacle on the backplane, the flatnature of the contact surface between the lens array and the opticalreceptacle and optical waveguide interface on the backplane ensures thatlight signals can be communicated from the connector to the backplanewith little distortion. Accordingly, a GRIN lens array that effectivelyhas a substantially flat surface that engages with the opticalreceptacle and optical waveguide interface is particularly suitable foruse in this application. The lenses serve to image light beingtransmitted from the user circuit into a point on the waveguideinterface and also to collimate light received from the waveguide on tothe user circuit.

FIG. 7 shows a plan view of a schematic representation of a GRIN lensarray arranged on an array holder 38, in this case a ceramic holder. Thephotonic interface unit will also comprise one or more light sources andreceivers such as VCSEL and PIN arrays. In the example shown, two slots40 are provided for receiving the MT pins of the MT pin block 36 (notshown in FIG. 7). The GRIN lens array 42 is arranged between the MT pinslots 40.

The separation of the MT pin slots 40 is fixed at 4.6 mm to correspondwith the standard separation of a pair of MT pins. The GRIN lens array42 is off-set (in this specific example by 0.745 mm) from the centreline of the MT slots. This is selected to correspond to the off-set ofthe waveguides in the optical backplane to the centre line of the MT pinslots in the optical mount.

The ceramic holder 38 incorporates the slots 40 to accommodate the MTpins protruding through the flexible circuit board 16. The positionalalignment of these slots 40 with respect to the lens array, correspondto the alignment of the MT pins to the VCSEL and PIN arrays, thusproviding initial self-alignment of the lens array to the associatedphotonics. Accordingly, the arrangement shown in FIG. 7 is aparticularly suitable and convenient form of lens array to use.

During passive assembly of the GRIN lenses under a microscope, a clearimage of the underlying VCSEL and photodiode die is visible. Visualalignment of the centre of the lenses to the centre of the visibleactive areas of these die is therefore both easy and sufficientlyaccurate.

It will be appreciated that numerous modifications to and departuresfrom the preferred embodiments described above will occur to thosehaving skill in the art. Thus, it is intended that the present inventioncovers the modifications and variations of the invention, provided theycome within that spirit and scope of the appended claims and theirequivalents.

1. An optical connector for connecting a user circuit to an opticalbackplane, in use the connector being adapted for mounting on a usercircuit, the connector comprising: an optical interface through whichoptical signals may be transmitted and received between a user circuitand a said optical backplane; a primary aligner for engagement with acorresponding aligner on a backplane to ensure alignment of the opticalinterface with the backplane; a support for supporting the alignerand/or the optical interface on the connector, the support beingselected to enable relative movement between a user circuit to which theconnector is connected in use and the aligner and/or the opticalinterface; and a movement mechanism for urging engagement of the primaryaligner on the connector with the aligner of the backplane, in which thesupport comprises a flexible substrate having a first end fixedlymounted to the connector and a second end movable relative to the firstend and in which the movement mechanism comprises a cam movable to urgethe flexible substrate into an engagement position in which, in use, theprimary aligner is engaged with the corresponding aligner on thebackplane.
 2. An optical connector according to claim 1, in which thealigner on the connector comprises at least one projection forengagement in a socket on a backplane.
 3. An optical connector accordingto claim 2, comprising a secondary aligner for ensuring that the primaryaligner is in a position where it can be brought into registration withthe corresponding aligner on the backplane.
 4. An optical connectoraccording to claim 1, wherein the optical interface includes one or morelenses for imaging or collimating light signals sent to or from theoptical interface, the one or more lenses have a flat external surface.5. An optical connector according to claim 4, wherein the one or morelenses is a graded index lens array.
 6. An optical connector forconnecting a user circuit to an optical backplane, in use the connectorbeing adapted for mounting on a user circuit, the connector comprising:an optical interface through which optical signals may be transmittedand received between a user circuit and a said optical backplane; aprimary aligner for engagement with a corresponding aligner on abackplane to ensure alignment of the optical interface with thebackplane; and a support for supporting the aligner and/or the opticalinterface on the connector, the support being selected to enablerelative movement between a user circuit to which the connector isconnected in use and the aligner and/or the optical interface, amovement mechanism for urging engagement of the primary aligner on theconnector with the aligner on the backplane, the movement mechanismbeing arranged to move the primary aligner in a direction substantiallyperpendicular to the plane of the user circuit, and an opticaltransceiver on board the connector.
 7. An optical connector according toclaim 6, in which the aligner on the connector comprises at least oneprojection for engagement in a socket on a backplane.
 8. An opticalconnector according to claim 7, comprising a secondary aligner forensuring that the primary aligner is in a position where it can bebrought into registration with the corresponding aligner on thebackplane.
 9. An optical connector according to claim 6, in which thesupport comprises a flexible substrate having a first end fixedlymounted to the connector and a second end movable relative to the firstend.
 10. An optical connector according to claim 6, wherein the opticalinterface includes one or more lenses for imaging or collimating lightsignals sent to or from the optical interface, the one or more lenseshave a flat external surface.
 11. An optical connector according toclaim 10, wherein the one or more lenses is a graded index lens array.12. A method of connecting a user circuit to an optical backplane, themethod comprising: providing a user circuit having a connector arrangedthereon, the connector being an optical connector for connecting a usercircuit to an optical backplane, in use the connector being adapted formounting on a user circuit, the connector comprising: an opticalinterface through which optical signals may be transmitted and receivedbetween a user circuit and a said optical backplane; a primary alignerfor engagement with a corresponding aligner on a backplane to ensurealignment of the optical interface with the backplane; a support forsupporting the aligner and/or the optical interface on the connector,the support being selected to enable relative movement between a usercircuit to which the connector is connected in use and the alignerand/or the optical interface; and an optical transceiver on board theconnector; providing an optical backplane having one or more sockets forreceiving a connector; and engaging the connector with the socket of thebackplane by inserting the connector on a user circuit into one of thesockets and urging engagement of the aligner by causing it to move in adirection substantially perpendicular to the plane of the user circuit.13. A method according to claim 10, comprising, once the connector isengaged with the socket, activating a fixing unit to fix the connectorin a fixed relationship with the backplane.
 14. A method according toclaim 13, wherein the step of activating a fixing unit comprises turninga cam so that the connector locks into engagement with the backplane.15. A communication system comprising: an optical backplane forreceiving one or more user circuits for connection to the opticalbackplane; and, a connector for connecting the or each user circuit tothe optical backplane, wherein the connector is an optical connector forconnecting a user circuit to an optical backplane, in use the connectorbeing adapted for mounting on a user circuit, the connector comprising:an optical interface through which optical signals may be transmittedand received between a user circuit and a said optical backplane; aprimary aligner for engagement with a corresponding aligner on abackplane to ensure alignment of the optical interface with thebackplane; a support for supporting the aligner and/or the opticalinterface on the connector, the support being selected to enablerelative movement between a user circuit to which the connector isconnected in use and the aligner and/or the optical interface, amovement mechanism for urging engagement of the primary aligner on theconnector with the aligner on the backplane, the movement mechanismbeing arranged to move the primary aligner in a direction substantiallyperpendicular to the plane of the user circuit, and an opticaltransceiver on board the connector.